Evidence of peripheral nonlinearity in psychometric function slopes of forward-masked tones at 250 and 4000 Hz

Abstract

Results from this laboratory suggest that the compressive nonlinearity of the basilar membrane is reflected in slopes of psychometric functions (PFs) for forward-masked tones of 4000 Hz. Briefly, as the signal level at the threshold increases, slopes of PFs decrease. Many other behavioral measures have suggested significant nonlinearity at high frequencies, but results are less consistent at low frequencies. The purpose of the current study was to use a PF slope to investigate nonlinearity using low- and high-frequency stimuli in the same normal-hearing adults. Signals were 250 or 4000 Hz, 10-ms (5-ms rise/fall) duration, presented with a 10-ms delay. The on-frequency forward-maskers were 200-ms (2-ms rise/fall), presented at levels of 30-, 50-, 70-, and 90-dB SPL in separate conditions. A two-track, two-interval-forced-choice adaptive procedure was used, with decision rules to estimate 71% correct on one track, and 87% on the other track. Data from both tracks were combined to estimate PF slopes. PF slopes were steeper in low-threshold conditions and shallower in high-threshold conditions for both frequencies. These results suggest a significant nonlinearity at 250 Hz. [Work supported by NIDCD.]